U.S. patent application number 10/354658 was filed with the patent office on 2003-07-31 for laser apparatus, exposure apparatus and method.
Invention is credited to Nagai, Yoshiyuki.
Application Number | 20030142715 10/354658 |
Document ID | / |
Family ID | 27606407 |
Filed Date | 2003-07-31 |
United States Patent
Application |
20030142715 |
Kind Code |
A1 |
Nagai, Yoshiyuki |
July 31, 2003 |
Laser apparatus, exposure apparatus and method
Abstract
There is to provide a laser apparatus that emits a laser beam by
exciting gas enclosed in a chamber, including a gas characteristic
detecting mechanism for detecting a characteristic of the gas in
the chamber, and a calculation mechanism for calculating an
oscillation wavelength and/or a wavelength spectral bandwidth of
the laser beam based on a detected result by the gas characteristic
detecting mechanism.
Inventors: |
Nagai, Yoshiyuki; (Tochigi,
JP) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
345 PARK AVENUE
NEW YORK
NY
10154
US
|
Family ID: |
27606407 |
Appl. No.: |
10/354658 |
Filed: |
January 30, 2003 |
Current U.S.
Class: |
372/55 |
Current CPC
Class: |
H01S 3/1305 20130101;
H01S 3/225 20130101; H01S 3/134 20130101 |
Class at
Publication: |
372/55 |
International
Class: |
H01S 003/22; H01S
003/223 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 31, 2002 |
JP |
2002-023632 |
Claims
What is claimed is:
1. A laser apparatus that emits a laser beam by exciting gas
enclosed in a chamber, said laser apparatus comprising: a gas
characteristic detecting mechanism for detecting a characteristic
of the gas in the chamber; and a calculation mechanism for
calculating an oscillation wavelength and/or a wavelength spectral
bandwidth of the laser beam based on a detected result by the gas
characteristic detecting mechanism.
2. A laser apparatus according to claim 1, wherein said gas
characteristic detecting mechanism is a pressure sensor for
detecting a pressure of the gas in the chamber.
3. A laser apparatus according to claim 1, wherein said gas
characteristic detecting mechanism is a temperature sensor for
detecting a temperature of the gas in the chamber.
4. A laser apparatus according to claim 1, further comprising a
controller for determining whether an oscillation wavelength and/or
a wavelength spectral bandwidth of the laser beam fall within a
permissible range, and for generating correction information that
enables the oscillation wavelength and/or the wavelength spectral
bandwidth of the laser beam to fall within the permissible
range.
5. A laser apparatus according to claim 1, wherein the laser beam
oscillates at a wavelength of about 157 nm or shorter.
6. An exposure apparatus that uses a laser beam to exposure a
pattern on a mask, onto an object, said exposure apparatus
comprising: a laser apparatus for exciting gas to emit the laser
beam, said laser apparatus including a gas characteristic detecting
mechanism for detecting a characteristic of the gas enclosed in a
chamber; and a correction mechanism for correcting the exposure
based on a detected result by the gas characteristic detecting
mechanism.
7. An exposure apparatus according to claim 6, further comprising a
calculation mechanism for calculating an oscillation wavelength
and/or a wavelength spectral bandwidth of the laser beam based on a
detected result by the gas characteristic mechanism.
8. An exposure apparatus according to claim 7, wherein said
calculation mechanism is provided in said laser apparatus.
9. An exposure apparatus according to claim 7, wherein said
calculation mechanism is provided outside said laser apparatus.
10. An exposure method that uses a laser beam generated by exciting
gas enclosed in a chamber to expose a pattern on a mask, onto an
object, said exposure method comprising the steps of: detecting a
characteristic of the gas in the chamber; and determining whether
the exposure is to continue or stop based on a detected result by
said detecting step.
11. An exposure method according to claim 10, wherein said
detecting step comprises the step of calculating an oscillation
wavelength and/or a wavelength spectral bandwidth of the laser beam
from the characteristic.
12. An exposure method according to claim 10, wherein said
determining step comprises the step of comparing the detected
result by said detecting step, with a permissible range.
13. An exposure method according to claim 10, further comprising
the step of changing the characteristic of the gas in the chamber
when said determining step determines that the exposure is to
stop.
14. An exposure method according to claim 13, wherein said gas
characteristic changing step changes a pressure and/or temperature
of the gas in the chamber.
15. An exposure method that uses a laser beam generated by exciting
gas enclosed in a chamber to expose a pattern on a mask, onto an
object, said method comprising the steps of: detecting a
characteristic of the gas in the chamber; calculating an
oscillation wavelength and/or a wavelength spectral bandwidth of
the laser beam from the characteristic detected by said detecting
step; and correcting the exposure based on the calculated
oscillation wavelength.
16. An exposure method according to claim 15, wherein said
correcting step corrects an optical characteristic of a projection
optical system which projects the pattern on the mask onto the
object.
17. An exposure method according to claim 15, wherein said
correcting step moves the object along an optical axis.
18. A database for calculating, from a characteristic of a gas
enclosed in a chamber, an oscillation wavelength of a laser beam
generated by exciting the gas.
19. A database according to claim 18, wherein the characteristic
includes a pressure and/or temperature of the gas.
20. A database for calculating, from a characteristic of a gas
enclosed in a chamber, a wavelength spectral bandwidth of a laser
beam generated by exciting the gas.
21. A database according to claim 20, wherein the characteristic
includes a pressure and/or temperature of the gas.
22. A device fabrication method comprising the steps of: exposing a
pattern on a mask, onto an object by using an exposure apparatus
that uses a laser beam and includes a laser apparatus that excites
gas to emit the laser beam and includes a gas characteristic
detecting mechanism for detecting a characteristic of a gas
enclosed in a chamber, and a correction mechanism for correcting
the exposure based on a detected result by the gas characteristic
detecting mechanism; and performing a predetermined process for the
exposed object.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to laser
apparatuses, and more particularly to a laser apparatus in an
exposure apparatus that illuminates a mask or reticle (these terms
are used interchangeably in this application) which forms a pattern
for use with a lithography process for fabricating semiconductor
elements, liquid crystal display devices (LCD), image pick-up
devices (such as CCDs, etc.), thin-film magnetic heads, and the
like.
[0002] Along with recent demands on smaller and lower profile
electronic devices, fine semiconductor devices to be mounted onto
these electronic devices have been increasingly in demand. As a
transfer (lithography) method for fabricating semiconductor
devices, a projection exposure apparatus has been used
conventionally.
[0003] A critical dimension (or resolution) transferable by a
projection exposure apparatus is in proportion to the wavelength of
light to be used for exposure. Therefore, in recent years, the
exposure light source is in transition from the conventional
ultra-high pressure mercury lamp (including g-line (with a
wavelength of about 436 nm) and i-line (with a wavelength of about
365 nm)) to a KrF excimer laser with a shorter wavelength (i.e., a
wavelength of about 248 nm) to the ArF excimer laser (with a
wavelength of about 193 nm), and practical use of the F.sub.2 laser
(with a wavelength of about 157 nm) is also being promoted.
[0004] Optical elements that efficiently transmit light in such a
wavelength range (i.e., in the ultraviolet region) are limited to
certain glass materials such as synthetic quartz, calcium fluoride,
etc., and thus it is difficult to correct chromatic aberration.
Therefore, in using the KrF excimer laser and the ArF excimer laser
for an exposure light source, a wavelength spectral bandwidth of
about 300 pm at full width at half maximum in a spontaneous
oscillation state is generally turned to a narrowband of, e.g.,
about 0.5 pm, and feedback control (or wavelength control) is
provided by a wavelength selection element in a resonator such that
a laser beam may be always oscillated with a desired wavelength
while the wavelength is monitored.
[0005] On the other hand, in using the F.sub.2 laser as an exposure
light source, it is impossible to turn a wavelength spectral
bandwidth into a narrowband or to provide the wavelength control
for technical reasons: including multiple oscillation spectra
existing in the neighborhood of 157 nm; its wavelength spectral
bandwidth in a spontaneous oscillation state as much as about 1 pm,
i.e., narrower than the KrF excimer laser and the ArF excimer
laser; difficult turning of the laser beam into a narrower band
since the performance of an optical element used for a wavelength
bandwidth of 157 nm has not been satisfactory enough to be put into
practical use, difficult measurement of a wavelength and a
wavelength spectral bandwidth with high precision inside a laser
apparatus, and so on. Accordingly, the line selection method has
been proposed which selects, from among several wavelengths
oscillated in the F.sub.2 laser, only one wavelength for
oscillation.
[0006] The F.sub.2 and other excimer laser generally require a
laser apparatus that encloses halogen gases such as fluorine, etc.,
and rare gases such as helium, neon, etc. in a chamber, and uses
electric discharges produced by applying high voltage between the
electrodes disposed in the chamber to excite gases, thus
oscillating the laser beam. The continuous oscillation of the laser
beam would lower the concentration of the halogen gas because the
halogen gas would react on impurities present in the chamber, or be
absorbed by the inner wall of the chamber. Therefore, a
compositional ratio of the laser gas varies from its optimum ratio,
thereby causing pulse energy (or laser oscillation efficiency) to
be lowered.
[0007] Accordingly, the pulse energy of the laser beam is kept at a
desired value by raising the voltage to be applied between the
electrodes, or by insufflating a specified amount of gas including
halogen gas (gas injection) to raise the gas pressure in the
chamber when a rising amount of the applied voltage reaches a
certain threshold. However, the repetitive gas injection would
increase impurities in the chamber, and facilitate interaction
between the impurities and halogen. As a result, the pulse energy
cannot be maintained at a desired value even with the increased
voltage to be applied between the electrodes rises and gas
injection, because. When the gas injection becomes less effective,
the majority of the gas in the chamber is exhausted and fresh gas
is injected (gas exchange). In other words, the F.sub.2 and other
excimer laser obtain a desired output by changing the gas pressure
and/or the partial pressure of fluorine in the chamber or by
raising the voltage applied between the electrodes, depending on
the use circumstances.
[0008] In case of the F.sub.2 laser, it has become evident that as
gas characteristics such as its pressure and temperature in a
chamber vary because of gas injection, etc., the oscillation
wavelength and wavelength spectral bandwidth of the laser beam will
change accordingly.
[0009] Accordingly, when the F.sub.2 laser is used as an exposure
light source, its oscillation wavelength and wavelength spectral
bandwidth will change during exposure. If they exceed, e.g.,
wavelength stability and a tolerance of the wavelength spectral
bandwidth required by an exposure system, it becomes difficult to
achieve desired resolution required for the exposure apparatus.
[0010] Moreover, when the F.sub.2 laser is used, it is difficult to
directly confirm whether or not the laser beam exhibits its desired
performance during exposure, because the measurement of a
wavelength is technically very difficult in a laser apparatus with
high accuracy. The direct confirmation of the oscillation
wavelength, if any, would clearly give an adverse impact onto the
productivity of the exposure apparatus in running cost and
maintenance frequency in light of the current durability of a
current optical element. A similar problem arises when a laser that
oscillates in a wavelength shorter than the F.sub.2 laser is used
as a light source.
BRIEF SUMMARY OF THE INVENTION
[0011] Accordingly, it is an exemplified object of the present
invention to provide a laser apparatus, and an exposure apparatus
and method, which indirectly detect a change in an oscillation
wavelength and wavelength spectral bandwidth of a laser beam, and
maintain predetermined optical performance.
[0012] A laser apparatus as one aspect of the present invention,
which emits a laser beam by exciting gas enclosed in a chamber
includes a gas characteristic detecting mechanism for detecting a
characteristic of the gas in the chamber, and a calculation
mechanism for calculating an oscillation wavelength and a
wavelength spectral bandwidth of the laser beam based on a detected
result by the gas characteristic detecting mechanism.
[0013] The gas characteristic detecting mechanism may be a pressure
sensor for detecting a pressure of the gas in the chamber, or a
temperature sensor for detecting a temperature of the gas in the
chamber. The laser apparatus may further include a controller for
determining whether an oscillation wavelength and/or a wavelength
spectral bandwidth of the laser beam fall within a permissible
range, and for generating correction information that enables the
oscillation wavelength and/or the wavelength spectral bandwidth of
the laser beam to fall within the permissible range. The laser beam
may oscillate at a wavelength of about 157 nm or shorter.
[0014] An exposure apparatus of another aspect of the present
invention, which uses a laser beam to exposure a pattern on a mask,
onto an object includes a laser apparatus for exciting gas to emit
the laser beam, the laser apparatus including a gas characteristic
detecting mechanism for detecting a characteristic of the gas
enclosed in a chamber, and a correction mechanism for correcting
the exposure based on a detected result by the gas characteristic
detecting mechanism.
[0015] The exposure apparatus may further include a calculation
mechanism for calculating an oscillation wavelength and a
wavelength spectral bandwidth of the laser beam based on a detected
result by the gas characteristic mechanism. The calculation
mechanism may be provided inside or outside the laser
apparatus.
[0016] An exposure method of still another aspect of the present
invention, which uses a laser beam generated by exciting gas
enclosed in a chamber to expose a pattern on a mask, onto an object
includes the steps of detecting a characteristic of the gas in the
chamber, and determining whether the exposure is to continue or
stop based on a detected result by the detecting step.
[0017] The detecting step may include the step of calculating an
oscillation wavelength and/or a wavelength spectral bandwidth of
the laser beam from the characteristic. The determining step may
include the step of comparing the detected result by the detecting
step, with a permissible range.
[0018] The exposure method may further include the step of changing
the characteristic of the gas in the chamber when the determining
step determines that the exposure is to stop. The gas
characteristic changing step may change a pressure and/or
temperature of the gas in the chamber.
[0019] An exposure method of another aspect of the present
invention, which uses a laser beam generated by exciting gas
enclosed in a chamber to expose a pattern on a mask, onto an object
includes the steps of detecting a characteristic of the gas in the
chamber, calculating an oscillation wavelength and/or a wavelength
spectral bandwidth of the laser beam from the characteristic
detected by the detecting step, and correcting the exposure based
on the calculated oscillation wavelength.
[0020] The correcting step may correct an optical characteristic of
a projection optical system which projects the pattern on the mask
onto the object. The correcting step may move the object along an
optical axis.
[0021] A database for calculating, from a characteristic of a gas
enclosed in a chamber, an oscillation wavelength or wavelength
spectral bandwidth of a laser beam generated by exciting the gas
may constitute another aspect of the present invention. In these
databases, the characteristic may include a pressure and/or
temperature of the gas.
[0022] A device fabrication method of another aspect of the present
invention include the steps of exposing a pattern on a mask, onto
an object by using the above exposure apparatus, and performing a
predetermined process for the exposed object. Claims for the device
fabrication method that exhibits operations similar to those of the
above exposure apparatus cover devices as their intermediate
products and finished products. Moreover, such devices include
semiconductor chips such as LSIs and VLSIs, CCDs, LCDs, magnetic
sensors, thin-film magnetic heads, etc.
[0023] Other objects and further features of the present invention
will become readily apparent from the following description of the
embodiments with reference to accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a schematic block diagram of an exposure apparatus
as one aspect of the present invention.
[0025] FIG. 2 is a schematic block diagram of a laser apparatus as
one aspect of the present invention.
[0026] FIG. 3 is a flowchart for explaining how to obtain an
oscillation wavelength and wavelength spectral bandwidth of a laser
beam in an experimental way when changing the gas pressure and gas
temperature in the chamber in the laser apparatus shown in FIG.
2.
[0027] FIG. 4 is a graph showing a relationship between the gas
characteristic of the laser apparatus shown in FIG. 2 and an
oscillation wavelength of the laser beam.
[0028] FIG. 5 is a graph showing the relationship between the gas
characteristic of the laser apparatus shown in FIG. 2 and a
wavelength spectral bandwidth of the laser beam.
[0029] FIG. 6 is a flowchart for explaining a process when an
oscillation wavelength or wavelength spectral bandwidth of a laser
beam oscillated from the laser apparatus shown in FIG. 2 becomes
out of permissible range.
[0030] FIG. 7 is a flowchart for explaining a device fabrication
method using an inventive exposure apparatus.
[0031] FIG. 8 is a detailed flowchart for Step 4 shown in FIG.
7.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] Referring now to accompanying drawings, a description will
be given of an exposure apparatus 1 and a laser apparatus 100 as
aspects of the present invention. However, the present invention is
not limited to these embodiments, and each element may be replaced
within a scope of this invention. Here, FIG. 1 is a schematic block
diagram of the exposure apparatus 1 as one aspect of the present
invention. As shown in FIG. 1, the inventive exposure apparatus 1
includes the laser apparatus 100, an illumination optical system
200, a mask 300, a projection optical system 400, a plate 500, a
stage 600, and a controller 700.
[0033] The exposure apparatus 1 is a projection exposure apparatus
that exposes onto the plate 500 a circuit pattern created on the
mask 300, e.g., in a step-and-repeat or a step-and-scan manner.
Such an exposure apparatus is suitable for a submicron or
quarter-micron lithography process, and this embodiment exemplarily
describes a step-and-scan exposure apparatus (which is also called
"a scanner"). "The step-and-scan manner", as used herein, is an
exposure method that exposes a mask pattern onto a wafer by
continuously scanning the wafer relative to the mask, and by
moving, after a shot of exposure, the wafer stepwise to the next
exposure area to be shot. "The step-and-repeat manner" is another
mode of exposure method that moves a wafer stepwise to an exposure
area for the next shot every shot of cell projection onto the
wafer.
[0034] The laser apparatus 100 includes, as shown in FIG. 2, a
controller 102, a high-voltage light source 104, a compression
circuit 106, a chamber 108, apertures 112a and 112b, a line
selection module 114, a partially transparent mirror 116, a beam
splitter 118, a shutter 120, a light monitor section 122, a
pressure sensor 124, a temperature sensor 126, a calculator 128,
and a gas controller 130, thus emitting, e.g., the F.sub.2 laser
(with a wavelength of about 157 nm) that emits pulsed light or a
laser beam that oscillates at a shorter wavelength. Here, FIG. 2 is
a schematic block diagram of the laser apparatus 100 as another
aspect of the present invention.
[0035] The controller 102 receives a trigger signal, energy
command, or an applied voltage command all sent from the controller
700 in the exposure apparatus 1. Based on such signals, the
controller 102 sends a high voltage signal to the high voltage
light source 104, as well as sending the trigger signal to the
compression circuit 106 at a timing of emitting a laser beam.
[0036] There are provided discharge electrodes 108a and 108b in the
chamber 108, in which as a laser gas, halogen gases such as
fluorine, etc., and rare gases such as helium, neon, etc. are
injected at a specified rate.
[0037] If a high voltage of as much as 10.about.30 kV is applied
between the discharge electrodes 108a and 108b (to the area 108c)
by the compression circuit 106, electric discharge takes place in
this area 108c, and excites laser gas injected in the chamber 108,
thus emitting light between the discharge electrodes 108a and 108b
(area 108c).
[0038] Light generated between the discharge electrodes 108a and
108b (the area 108c) is amplified while passing through windows
110a and 110b and the apertures 112a and 112b, and going back and
forth between a rear mirror (not shown) inside the line selection
module 114 and the partial transparent mirror 116, thus growing to
be a laser beam.
[0039] The line selection module 114 houses a wavelength selection
element such as a prism, which selects light only with a specific
wavelength from among multiple wavelengths oscillated in the
F.sub.2 laser, and reflects it to the chamber 108. Thus, a laser
beam is emitted with such a wavelength. Any reflected light of
another wavelength is intercepted by the apertures 112a and 112b,
and not output as a laser beam.
[0040] Most generated laser beam transmit the beam splitter 118,
and outgoes to the shaping optical system 202 of the illumination
optical system 202 when the shutter 120 opens. Some of the laser
beams reflected at the beam splitter 118 are introduced into the
light monitor section 122.
[0041] The light monitor section 122 monitors light energy per
pulse, and sends these results to the controller 102. The
controller 102 determines the voltage applied for pulsed light to
be generated next time based on the energy measurement result from
the light monitor section 122 or energy control information sent
from the controller 700 of the exposure apparatus 1.
[0042] The chamber 108 is provided with the pressure sensor 124
that measures the pressure of the gas in the chamber 108 and the
temperature sensor 126 that measures the temperature of the gas in
the chamber 108, so as to measure the gas pressure and temperature
in the chamber 108 constantly or at a specified timing. Measurement
results of the pressure and temperature of the gas in the chamber
108 are sent to the calculator 128 that calculates the oscillation
wavelength and wavelength spectral bandwidth of a laser beam. The
calculator 128 calculates the oscillation wavelength and wavelength
spectral bandwidth of the laser beam based on the measured results
from the pressure sensor 124 and the temperature sensor 126, and
sends the result to the controller 102.
[0043] The result of the oscillation wavelength and wavelength
spectral bandwidth of the laser beam is also sent, as needed, from
the controller 102 to the controller 700 in the exposure apparatus
1. As described later, in order to calculate the oscillation
wavelength and wavelength spectral bandwidth of the laser beam, the
calculator 128 is required to store a relational expression from
the correlation between gas characteristics such as the pressure
and temperature of the gas and the oscillation wavelength and
wavelength spectral bandwidth, which relationship has been
obtainable through an experiment.
[0044] This embodiment provides the laser apparatus 100 with the
calculator 128 for calculating the oscillation wavelength and
wavelength spectral bandwidth of a laser beam based on the
measurement results of the pressure sensor 124 and the temperature
sensor 126, but the controller 700 of the exposure apparatus 1 may
have a unit for calculating both or at least either one of the
oscillation wavelength and wavelength spectral bandwidth of a laser
beam based on gas characteristics. In that case, the results of the
gas characteristics measured by the pressure sensor 124 and the
temperature sensor 126 are sent directly to the controller 102, and
are converted into the oscillation wavelength and wavelength
spectral bandwidth at the controller 700 in the exposure apparatus
1 from the controller 102.
[0045] When a laser beam continues to oscillate, the laser gas
gradually deteriorates in the chamber 108 such that the ratio of
its halogen gas drops and impurities increase. Therefore, it is
necessary to inject gas including halogen gas periodically into the
chamber 108 (hereinafter "gas injection"), or to exchange the major
part of the laser gas in the chamber 108 ("gas exchange"
hereinafter).
[0046] When gas injection or gas exchange is necessary, the gas
controller 130 introduces fresh gas into the chamber 108 via a
laser gas pipe 132, or exhausts a part or major part of the
deteriorated gas from the chamber 108 via an exhausting gas pipe
134.
[0047] Referring now to FIG. 3, a description will be given of an
example of how to experimentally derive a relationship between gas
characteristics in the chamber 108 and the oscillation wavelength
and wavelength spectral bandwidth of the laser beam. FIG. 3 is a
flowchart for explaining a method 1000 that experimentally obtains
an oscillation wavelength and wavelength spectral bandwidth of a
laser beam when the gas pressure and gas temperature are changed in
the chamber 108. A spectrometer is used to measure the oscillation
wavelength and wavelength spectral bandwidth of the laser beam
oscillated from the laser apparatus 100.
[0048] First, the laser apparatus 100 start oscillation (Step 1002)
to introduce a laser beam into the spectrometer. Then, the gas
temperature (Step 1004) and gas pressure (Step 1005) are measured
in the chamber 108, and the spectrometer measures the oscillation
wavelength and wavelength spectral bandwidth of the laser beam at
approximately the same time or at an immediately later timing (Step
1008).
[0049] Next, while the gas temperature is maintained constant, the
gas pressure in the chamber 108 is changed and it is determined
whether the oscillation wavelength and wavelength spectral
bandwidth of the laser beam is to continue or stop (Step 1010).
When the measurement is to continue, the gas pressure in the
chamber 108 is changed (Step 1012), the gas pressure is measured
again (1016), and then the oscillation wavelength and wavelength
spectral bandwidth of the laser are measured again (Step 1008).
[0050] When data gathering of the gas pressure range to be used by
the laser apparatus 100 is completed, the measurement at the same
gas temperature stops and it is determined whether the oscillation
wavelength and wavelength spectral bandwidth of the laser beam is
to continue or stop by changing the gas temperature in the chamber
108 (Step 1014). When the measurement is to continue, the gas
temperature in the chamber 108 is changed (Step 1016). The gas
temperature may be changed by changing the oscillation frequency of
the laser beam, or by controlling the temperature through a
temperature control device in the chamber 108 such as a heater.
[0051] After the gas temperature changes, the gas pressure is
changed again while the gas temperature is maintained constant, and
the oscillation wavelength and wavelength spectral bandwidth of the
laser beam are measured (repeat the procedure after Step 1004).
When data gathering of the gas pressure range to be used by the
laser apparatus 100 is completed, the laser oscillation stops (Step
1018), and the operation ends (Step 1020).
[0052] FIGS. 4 and 5 show exemplary data obtained by this method
1000. FIG. 4 is a graph of a relationship between the gas
characteristics of the laser apparatus 100 (the gas pressure and
temperature) and the oscillation wavelength of the laser beam,
where the abscissa axis is the gas pressure and the ordinate axis
is the oscillation wavelength, thus showing data by changing the
gas temperature like T.sub.a, T.sub.b, T.sub.c . . . . FIG. 5 is a
graph of a relationship between the gas characteristics of the
laser apparatus 100 (the gas pressure and gas temperature) and the
wavelength spectral bandwidth of the laser beam, where the abscissa
axis is the gas pressure and the ordinate axis is the wavelength
spectral bandwidth, showing data by changing the gas temperature
like T.sub.a, T.sub.b, T.sub.c . . . . Such data serve as a
database for calculating the oscillation wavelength or the
wavelength spectral bandwidth of the laser beam based on the
measured gas characteristics.
[0053] Referring to FIGS. 4 and 5, the oscillation wavelength A and
the wavelength spectral bandwidth .DELTA..lambda. of the laser
apparatus 100 may be estimated by the equation (function) shown
below where p is the pressure of the laser gas, and T is the
temperature of the laser gas:
.lambda.=f(p, T) (1) (Oscillation wavelength)
.DELTA..lambda.=g(p, T) (2) (Wavelength spectral bandwidth)
[0054] In practice, the function may be estimated from results
obtainable by implementing this method 1000 at a laser
manufacturer's plant or an exposure apparatus manufacturer's
plant.
[0055] The instant embodiment has typified the gas pressure and gas
temperature in the chamber 108 as items to be detected about gas
characteristics in finding the oscillation wavelength and
wavelength spectral bandwidth of the laser beam that the laser
apparatus 100 emits, but other gas characteristics may be used such
as gas composition ratio, etc. Of course, the oscillation
wavelength and wavelength spectral bandwidth may be derived from
detections of these characteristics together with the gas pressure
and gas temperature.
[0056] The calculator 128 stores the functions f (p, T) and g (p,
T) in the equations (1) and (2). The calculator 128 calculates the
oscillation wavelength of the laser beam each time using the
function f (p, T) and measured values of the gas pressure and gas
temperature in the chamber 108 obtained by the pressure sensor 124
and the temperature sensor 126. The calculator 128 sends this
calculation result to the controller 102, and the controller 102
sends, if needed, it to the controller 700 in the exposure
apparatus 1.
[0057] The calculator 128 calculates the wavelength spectral
bandwidth of the laser beam each time using the function g (p, T)
and measured values of the gas pressure and gas temperature in the
chamber 108 obtained by the pressure sensor 124 and the temperature
sensor 126. The calculator 128 sends this calculation result to the
controller 102, and the controller 102 sends, if needed, it to the
controller 700 in the exposure apparatus as required.
[0058] The controller 102 determines whether the oscillation
wavelength and wavelength spectral bandwidth the laser beam
calculated each time fall within permissible ranges. When the
controller 102 determines that the oscillation wavelength and
wavelength spectral bandwidth fall within the permissible ranges,
the exposure operation continues. On the other hand, when the
controller 102 determines that at least one of the oscillation
wavelength and the wavelength spectral bandwidth is out of
permissible range, it sends to the controller 700 in the exposure
apparatus 1 a signal informing that at least one of the oscillation
wavelength and the wavelength spectral bandwidth is out of the
permissible range. In response, the controller 700 stops the
exposure operation as well as taking steps so that the oscillation
wavelength and wavelength spectral bandwidth may fall within the
permissible range.
[0059] Turning back to FIG. 1, the illumination apparatus 200 is an
optical system for illuminating the mask 300, and includes, in
order along the optical path of the laser beam from the laser
apparatus 100, a beam shaping optical system 202 for shaping a
section of the laser beam into a desired shape, a variable ND
filter 204 for adjusting the intensity of the laser beam, an
optical integrator 206 for dividing and superimposing the laser
beam to make its intensity uniform on the surface of the mask 300,
a condenser lens 208 for condensing the laser beam via the optical
integrator 206, a beam splitter 212 for leading part of the laser
beam from the condenser lens 208 to a light detector 210, a masking
blade 214, arranged near a point where the laser beam is condensed
by the condenser lens 208, for regulating the range to irradiate
the laser beam onto the mask 300 plane, an imaging lens 216 for
forming an image of the masking blade 214 onto the mask 300, and a
mirror 218 for directing the optical path of the laser beam in the
direction of the projection optical system 400.
[0060] The mask 300 forms a circuit pattern (or an image) to be
transferred, and is supported and driven by a mask stage (not
shown). Diffracted light emitted from the mask 300 passes the
projection optical system 400, thus and then is projected onto the
plate 500. The mask 300 and the plate 500 are located in an
optically conjugate relationship. Since the exposure apparatus 1 of
this embodiment is a scanner, the mask 300 and the plate 500 are
scanned at the speed ratio of the demagnification ratio of the
projection optical system 400, thus transferring the pattern on the
mask 300 to the plate 500.
[0061] The projection optical system 400 demagnifies a circuit
pattern on the mask 300 at a specified magnification ratio (e.g.,
1/2.about.{fraction (1/10)}), thus projecting and exposing
(transferring) the pattern to one of multiple shot areas on the
plate 500. The projection optical system 400 may use an optical
system solely including a plurality of lens elements, an optical
system including a plurality of lens elements and at least one
concave mirror (a catadioptric optical system), an optical system
including a plurality of lens elements and at least one diffractive
optical element such as a kinoform, and a full mirror type optical
system, and so on. Any necessary correction of the chromatic
aberration may use a plurality of lens units made from glass
materials having different dispersion values (Abbe values), or
arrange a diffractive optical element such that it disperses in a
direction opposite to that of the lens unit.
[0062] The projection optical system 400 is provided with an
aberration correction unit 410. The projection optical system 400's
aberration produced by a fluctuation of the oscillation wavelength
of the laser beam may be corrected by driving some lenses in the
aberration correction unit 410 or by controlling a pressure between
specified lenses.
[0063] The plate 500 is an object to be exposed such as a wafer and
a liquid crystal plate, and photoresist is applied onto it. A
photoresist application step includes a pretreatment, an adhesion
accelerator application treatment, a photoresist application
treatment, and a pre-bake treatment. The pretreatment includes
cleaning, drying, etc. The adhesion accelerator application
treatment is a surface reforming process so as to enhance the
adhesion between the photo-resist and a base (i.e., a process to
increase the hydrophobicity by applying a surface active agent),
through a coat or vaporous process using an organic film such as
HMDS (Hexamethyl-disilazane). The pre-bake treatment is a baking
(or burning) step, softer than that after development, which
removes the solvent.
[0064] The stage 600 uses, for example, a linear motor to move the
plate 500 in a direction vertical to the optical axis of the
projection optical system 400. The mask 300 and plate 500 are, for
example, scanned synchronously, and the positions of the stage 600
and a mask stage (not shown) are monitored, for example, by a laser
interferometer and the like, so that both are driven at a constant
speed ratio. The stage 600 can also move the plate 500 in a
direction parallel to the optical axis of the projection optical
system 400, so that the plate is controlled such that the
image-forming position of the mask 300 and the surface of the plate
500 agree.
[0065] The stage 600 is installed on a stage surface plate
supported on the floor and the like, for example, via a damper, and
the mask stage and the projection optical system 400 are installed
on a body tube surface plate (not shown) supported, for example,
via a damper to the base-frame placed on the floor.
[0066] The controller 700 receives the oscillation wavelength and
wavelength spectral bandwidth of a laser beam sent from the laser
apparatus 100 (i.e., the oscillation wavelength and wavelength
spectral bandwidth of a laser beam calculated from the measured gas
characteristics), and based on this, drives an optical member (not
shown) in the aberration correction unit 410 of the projection
optical system 400 as required, controls the pressure between
specific lenses, corrects an interval between specified lenses, and
drives the stage 600, thus making an adjustment such that the
performance of image-forming a pattern on the mask 300 onto the
plate 500 is on a desired level. In other words, the controller 700
corrects aberration produced by a change of the oscillation
wavelength of a laser beam.
[0067] As described above, the laser apparatus 100 determines
whether the oscillation wavelength and wavelength spectral
bandwidth of the laser beam calculated from the measured gas
characteristics fall within the permissible ranges. When at least
one of the oscillation wavelength and wavelength spectral bandwidth
of the laser beam is out of permissible range, the controller 700
receives the signal indicating that at least one of the oscillation
wavelength and wavelength spectral bandwidth of the laser beam is
out of permissible range. Receiving such a signal, the controller
700 stops exposing a pattern to the plate 500, closes the shutter
120 located at the laser beam exit opening of the laser apparatus
100, and makes an adjustment so that the oscillation wavelength and
wavelength spectral bandwidth of the laser beam in the laser
apparatus 100 may fall within the permissible range. When the
adjustment finishes, the controller 700 opens the shutter 120, and
resumes the exposure onto the plate 500.
[0068] The controller 700 sends a trigger signal for the laser
apparatus 100 to emit a laser beam as well as processing
photo-electric conversion signals in accordance to the intensity of
the laser beam photo-electrically converted by the photo-detector
210. By integrating such photo-electric conversion signals, the
controller 700 sends to the laser apparatus 100 a signal of an
energy command or an applied voltage command for controlling an
amount of exposure. Based on such a signal, the laser apparatus 100
allows the controller 102 to control each unit and emit light with
predetermined energy as described above.
[0069] The controller 700 receives information from the laser
apparatus 100, which includes, in addition to the signal indicative
of a determination of whether the oscillation wavelength and
wavelength spectral bandwidth of a laser beam are within the
permissible ranges, a signal indicative of a determination of
whether energy stability is normal or abnormal, an interlock
signal, etc. Based on these signals, the controller 700 determines
whether the exposure operation is to continue or stop, and controls
the oscillation state of the laser apparatus 100.
[0070] Referring now to FIG. 6, a description will be given of a
treatment when the oscillation wavelength or wavelength spectral
bandwidth of a laser beam is out of permissible range. FIG. 6 is a
flowchart for explaining a process when the oscillation wavelength
or wavelength spectral bandwidth of a laser beam that the laser
apparatus 100 oscillates are out of permissible range. While the
laser beam oscillates, the oscillation wavelength and wavelength
spectral bandwidth of the laser beam are calculated from
measurement results sent to the calculator 128 constantly or at a
specific timing, of the pressure sensor 124 and the temperature
sensor 126, and such a calculation result is sent to the controller
102 (Step 2002). The controller 102 determines whether the
oscillation wavelength and wavelength spectral bandwidth fall
within the permissible ranges (Step 2004).
[0071] If the oscillation wavelength and wavelength spectral
bandwidth of a laser beam are within the permissible ranges, the
exposure operation continues uninterruptedly. If either one of the
oscillation wavelength and wavelength spectral bandwidth is out of
permissible range, the controller 102 sends to the controller 700
in the exposure apparatus 1 the signal indicating that at least one
of the oscillation wavelength and the wavelength spectral bandwidth
is out of permissible range (Step 2006). The controller 700 that
received the signal stop sending the laser apparatus 100 the
trigger signal for emitting light, and stops the exposure operation
(Step 2008).
[0072] Thereafter, the gas controller 130 changes the gas pressure
in the chamber 108 by exhausting the laser gas insufflated into the
chamber 108 in the laser apparatus 100, or filling the chamber 108
with fresh laser gas, thus making an adjustment so that it may have
the desired gas pressure (Step 2010). The calculator 128 in the
laser apparatus 100 calculates the oscillation wavelength and
wavelength spectral bandwidth of the laser from the gas
characteristics (gas pressure and gas temperature) after the
adjustment (Step 2012), and determines whether such calculation
results are well within the permissible range (Step 2014).
[0073] If at least one of the oscillation wavelength and the
wavelength spectral bandwidth is out of permissible range, the
steps from Step 2010 repeat, and the gas controller 130 changes the
gas pressure in the chamber 108 in the laser apparatus 100, thus
making an adjustment again so that it may have the desired gas
pressure. When both the oscillation wavelength and wavelength
spectral bandwidth of the laser beam are within the permissible
range, the controller 102 sends the calculated oscillation
wavelength and wavelength spectral bandwidth of the laser beam to
the controller 700 in the exposure apparatus 1 (Step 2016). Based
on the oscillation wavelength of the laser beam received from the
controller 102, the controller 700 adjusts the aberration
correction unit 410 of the projection optical system 400 or the
stage 600 (Step 2018), after which exposure to the plate 500 is
restarted (2020).
[0074] Whenever the laser gas used in the laser apparatus 100
deteriorates to change its characteristic in the chamber 108, e.g.,
after the gas injection or gas exchange, the calculator 128
calculates the oscillation wavelength and wavelength spectral
bandwidth of the laser beam are calculated based on the measurement
results of the pressure sensor 124 and the temperature sensor 126,
and such a calculation result is sent to the controller 102 and
controller 700 of the exposure apparatus 1. At this time, the
controller 700 also adjusts the aberration correction unit 410 in
the projection optical system 400 or the stage 600 (i.e., moves the
plate 500 along the optical axis of the projection optical system
400) based on the calculated oscillation wavelength and wavelength
spectral bandwidth of the laser beam. At this time, in order to
correct aberration produced by a change in the oscillation
wavelength of the laser beam, an optical member (not shown) in the
aberration correction unit 410 is driven, the pressure between
specified lenses is controlled, a specific lens interval is
corrected, or the stage 600 is driven along the optical axis of the
projection optical system 400. These operations may be performed
regularly, or when at least one of the oscillation wavelength and
wavelength spectral bandwidth of the laser beam exceed a preset
permissible variable amount.
[0075] During exposure, a beam emitted from the laser apparatus
100, e.g., Koehler-illuminates the mask 300 via the illumination
optical system 200. Light that passes through the mask 300 and
reflects the mask pattern is imaged onto the plate 500 by the
projection optical system 400. As described above, the laser
apparatus 100, which the exposure apparatus 1 uses, can indirectly
detect a change of the oscillation wavelength and wavelength
spectral bandwidth of the laser beam, and can exhibit a desired
resolution (i.e., stably emits a laser beam of a desired
oscillation wavelength and wavelength spectral bandwidth), thus
being able to provide devices (such as semiconductor devices, LCD
devices, photographing devices (such as CCDs, etc.), thin film
magnetic heads, and the like) with high throughput and economical
efficiency.
[0076] Referring now to FIGS. 7 and 8, a description will be given
of an embodiment of a device fabrication method using the above
mentioned exposure apparatus 1. FIG. 7 is a flowchart for
explaining how to fabricate devices (i.e., semiconductor chips such
as IC and LSI, LCDs, CCDs, and the like). Here, a description will
be given of the fabrication of a semiconductor chip as an example.
Step 1 (circuit design) designs a semiconductor device circuit.
Step 2 (mask fabrication) forms a mask having a designed circuit
pattern. Step 3 (wafer making) manufactures a wafer using materials
such as silicon. Step 4 (wafer process), which is also referred to
as a pretreatment, forms actual circuitry on the wafer through
lithography using the mask and wafer. Step 5 (assembly), which is
also referred to as a post-treatment, forms into a semiconductor
chip the wafer formed in Step 4 and includes an assembly step
(e.g., dicing, bonding), a packaging step (chip sealing), and the
like. Step 6 (inspection) performs various tests for the
semiconductor device made in Step 5, such as a validity test and a
durability test. Through these steps, a semiconductor device is
finished and shipped (Step 7).
[0077] FIG. 8 is a detailed flowchart of the wafer process in Step
4. Step 11 (oxidation) oxidizes the wafer's surface. Step 12 (CVD)
forms an insulating film on the wafer's surface. Step 13 (electrode
formation) forms electrodes on the wafer by vapor disposition and
the like. Step 14 (ion implantation) implants ion into the wafer.
Step 15 (resist process) applies a photosensitive material onto the
wafer. Step 16 (exposure) uses the exposure apparatus 300 to expose
a circuit pattern on the mask onto the wafer. Step 17 (development)
develops the exposed wafer. Step 18 (etching) etches parts other
than a developed resist image. Step 19 (resist stripping) removes
disused resist after etching. These steps are repeated, and
multi-layer circuit patterns are formed on the wafer. Use of the
fabrication method in this embodiment helps fabricate
higher-quality devices than ever.
[0078] So far, a description has been given of the preferred
embodiments of the present invention, but the present invention is
not limited to these preferred embodiments, and various
modifications and changes may be made in the present invention
without departing from the spirit and scope thereof.
[0079] Use of the laser apparatus makes it possible to indirectly
detect the oscillation wavelength and wavelength spectral bandwidth
of a laser beam, and make corrections based on these detected
results, thus exhibiting an expected resolution performance.
Therefore, an exposure apparatus and method having such a laser
apparatus can perform exposure operations with high throughput,
providing high quality devices.
* * * * *